In the production of brushes, after the bristle bundles have been inserted into the brush body, these bristle bundles are ground at their useful ends in order to obtain rounded off ends. This is necessary because, after they have been cut to length or sheared off the useful ends have sharp edges at the site of the cut. These sharp edges are undesirable, especially in the case of toothbrushes where they would lead to injury to the gums. For this reason, the rounding off of the useful ends has particular significance and importance, and the result of the rounding off is a fundamental quality factor for brushes, and toothbrushes in particular.
As already mentioned at the outset, the bristle ends can be sheared off and ground after the bristle bundles have been inserted into the brush bodies. In the case of brushes with so-called "welded" bristles, processing the bristle bundles before their joining with the brush body is already known from DE 38 20 372. To do this, the bristle bundles are held in clamping devices or the like, and their useful ends are ground and possibly given other additional processing steps. After this processing, the bristle bundles are conveyed to the brush body and joined to it.
In the case of brushes with comparatively long bristle bundles, this procedure can be employed largely without problem. What is a problem, however, is the processing of very short bristle bundles, which are used inter alia, for toothbrushes. Particularly in the case of bristle fields that are contoured and that have in certain areas bristle bundles which are shorter compared to the "normal bristle bundles," such bristle bundles are held for processing only with difficulty.
For the processing, and in particular for rounding off, the ends of the bristle bundles must project far enough beyond the clamping location that they are able to deflect laterally during the grinding. This is necessary in order to achieve sufficient rounding off of the ends.
It would be possible of course, in the case of processing short bristle bundles with small lateral deflection capability, to make use of shaped grinding tools or the like. However, such tools are expensive and also require exact positioning and guidance relative to the bristle bundle ends. Further, the result of the grinding is not satisfactory in all cases.
By means of the predetermined free clamping length, the varying lengths of the bristle bundles also yield correspondingly different rounding off results as well, since, due to the different free projecting lengths, the useful ends can also have different lateral deflections. Corresponding differences in quality of the bristles, even within a common bristle field, are the undesired consequence.
Grinding devices with essentially flat, rotating grinding surfaces have proven very effective in practice, whereby even large-area bristle fields or multiple bristle fields can be shaped simultaneously. In this case, special positioning is not necessary. In the case of flat or essentially flat grinding surfaces, though, sufficient lateral deflection of the bristle bundle ends is required for a good rounding off result.